Apparatus for treating small particle size materials



R. E. KING March 22, 1966 APPARATUS FOR TREATING SMALL PARTICLE SIZEMATERIALS 1 9 e 5 N s h E 9 S V m ,v e t n 9 d M r m m a S I h f 2 .M mR Y B Gas Filed May 51. 1961 R. E. KING March 22, 1966 APPARATUS FORTREATING SMALL PARTICLE SIZE MATERIALS 2 Sheets-Sheet 2 Filed May 31,1961 Pipe Jmmwev, in.

9 mm K vmr m M a m w R HfforneyS United States Patent Ofifice 3,Z4l,82iPatented Mar. 22, 1956 3,241,824 APPARATUS FOR TREATHNG SMALL PARTHCLElZE MATERIALS Richard E. King, Birmingham, Ala, assignor, by direct andmesne assignments, of one-half to W. S. Moore (10., a corporation ofMinnesota, and one-half to Northern Natural Gas (Jompany, a corporationof Delaware Filed May 31, 1961, Ser. No. 113,854 8 Claims. (Cl. 266-20)This invention relates to apparatus for treating small particle sizematerials and more particularly to apparatus for roasting fine particlesize materials, such as ore, and the like, and which is adapted forcarrying out the process described and claimed in the co-pendingapplication Serial No. 89,984, now abandoned, filed in my name and inthe name of Robert E. Lacey on February 17, 1961 and entitled Processfor Treating Fine Particle Size Materials.

An object of my invention is to provide apparatus for roasting fineparticle size materials, such as ferruginous ores, by completesuspension of the fine particles of material in a stream of hot reducinggases with the. particles of material flowing concurrently with thestream of reducing gases.

Another object of my invention is to provide apparatus for the chemicalreduction of small particle size ores in which the reduction takes placein a minimum of time and the apparatus required to handle the ore isreduced to a minimum.

Another object of my invention is to provide apparatus of the characterdesignated which shall be particularly adapted for the roasting ofnon-magnetic ores, such as hematite, oethite, and the like, whereby theyare converted into the oxide magnetite.

Another object of my invention is to provide apparatus of the characterdesignated which shall embody a multiple stage system in which the flowof solids and gas is concurrent within each stage, but the overall flowwithin the system is countercurrent, whereby the unreduced ore contactsthe depleted gas and becomes partially reduced before it contacts therich gas, thus bringing about faster and more complete reaction.

Another object of my invention is to provide apparatus of the characterdesignated which shall embody a multiple stage system in which at leastone stage is employed as a reactor with at least one other stageemployed as a preheate-r to effect heat economy.

A more specific object of my invention is to provide apparatus of thecharacter designated which shall include means for bringing about properflow of gases and solids through the apparatus without the use ofmechanical devices, therebymaking my apparatus adapted for troublefreeoperation at elevated temperatures.

A further object of my invention is to provide apparatus of thecharacter designated which shall be simple of construction, economicalof manufacture and which shall be adapted for hand-ling a large volumeof materials in a continuous manner.

As is well known in the art to which my invention relates, many ores,such as Mesabi slaty ore, cannot be smelted by the conventional typeblast furnace for the reason that the silica, alumina and othercompounds in the ore require the generation of a large volume of slagwhich increases the heat requirement in the furnace and lowers the yieldof metallic iron. Also, such ores are soft whereby upon handling orshipment, the ore disintegrates into small particles which areunsatisfactory for use in the blast furnace. Furthermore, the lowcontent of iron in such ores requires the shipment and handling ofalmost three parts by weight of ore to yield one part by weight ofmetallic iron.

There are large quantities of iron-bearing, low-grade ferruginous oresnow available which could constitute a great potential source of iron.The iron contained in many of these low-grade ores occurs largely in theoxide hematite or as hydrated oxides such as goethite or limonite, whichare not adapted for magnetic separation in the usual manner. By roastingthese iron oxides in a reducing atmosphere, the oxides are convertedinto magnetite which is magnetic and is recovered by magnetic separationin a manner well understood in the art. The reducing gases usuallyemployed are carbon monoxide, hydrogen or mixtures of these two gases.The gases are generally used in a mixture of other gases which resultfrom the partial combustion of fuel, such as natural gas, oil, coal orthe like.

Where intimate contact of the reducing gas and the solid iron oxide ismaintained at elevated temperatures, the reduction of the iron contentof the ore from hematite to magnetite proceeds rapidly. Accordingly, thesurf-aces of large particles of ore are readily contacted by thereducing gases and the gaseous reaction products are easily removedwhereby reduction of the oxides on the surface takes place rapidly. Onthe other hand, the iron oxides on the interior of a large particle ofore are not reduced as quickly due to the fact that the reducing gasmust diffuse through the solid material before it contacts the ironoxide. The product gas must then diffuse outwardly through the solidmaterial to escape from the reaction area and be replaced by reducinggas so that the reaction may continue. The rate of gas diffusion throughthe solid particles of ore thus becomes a major factor which limits thespeed of the reaction.

Apparatus heretofore employed for the roasting of iron ore has includedthe vertical shaft furnace, the

' rotary kiln, the multiple hearth furnace, the horizontal travelinggrate and the fluidized solid reactor. The size of the ore generallyemployed in all of the processes, other than the fluidized solidreactor, is substantially coarser than one-quarter inch and the reactionrequires long periods of time ranging from thirty minutes to severalhours to effect the desired reduction. The fluidized solid reactor mayprocess ore at a size finer than one-quarter inch but the gas velocitymust be sufliciently low to retain the solids in the reactor. Theproductive capacity of the reactor is thus limited by the rate at whichthe reducing gas can be supplied to the ore material and removedtherefrom.

Apparatus embodying features of my invention is illustrated in theaccompanying drawings, forming a part of this application, in which:

FIG. 1 is a flow sheet showing a two-stage system;

FIG. 2 is a chart showing a graphic representation that the gas pressuredeveloped at the bottom of an upwardly extending pipe by the flow ofsolids is directly proportional to the length of the pipe and thepressure developed increases with the increasing rate of solids flow anddecreasing pipe diameter; and,

FIG. 3 is a flow sheet showing the complete treatment of the materialsin a multi-state system.

Referring now to the drawings for a better understanding of myinvention, I show a two-stage system in FIG. 1 which comprises a firstupwardly extending riser 10 and a second upwardly extending riser 11. Agas inlet 12 is provided at the lower end of the riser 10 while theupper end of the riser 1t} communicates with a cyclone separator 13which separates the gas from the solid particles. The solid particlesare discharged from the cyclone separator 13 through a discharge conduit'14. Communicating with the gas discharge of the separator 13 is adownwardly extending conduit 17 which in turn communicates with thelower end of the second riser 11 \.9 whereby the stream of gasesindicated by the dotted arrow 18 are conveyed upwardly through thesecond riser 11. The upper end of the riser 11 communicates with acyclone separator 19 having a gas outlet 21 and an outlet 22 fordischarging solid particles.

The low ends of the risers and 11 are provided with 'venturi throats 23and 24, respectively. Communicating with the venturi 24- is an inletconduit 26 for supplying the small particle size materials to beroasted. The materials thus introduced through the conduit 26 areconveyed upwardly by the upwardly moving stream of gases, the flow ofthe solid particles being indicated by the solid arrows 27. As theconcurrently flowing stream of gas and solid particles pass through theseparator 19, the gases are discharged through the outlet 21 while thesolid particles are discharged downwardly through the outlet 22.

Communicating with the solid discharge outlet 22 is the upper end of aconduit 28. The lower end of the conduit 28 communicates with theventuri 23 whereby the solid particles are introduced into the lower endof the first riser 10.

From the foregoing description, the operation of the apparatus shown inFIG. 1 will be readily understood. The hot gases are continuouslyintroduced through the inlet 12 whereby they flow upwardly through theriser 10 and the separator 13 and then fiow downwardly through theconduit 17 to the venturi 24 at the lower end of the second riser 11.After passing through the venturi throat 24, the gaseous stream passesupwardly through the riser 11 and is finally discharged through theoutlet 21 of the separator 19. The solid materials are fed into theventuri 24 through the conduit 26 whereby they are conveyed upwardly andflow concurrently with the stream of gas to the separator 19. The solidparticles are discharged from the separator 19 through outlet 22 intothe conduit 28 whereupon the solids are introduced into the venturi 23of the riser 10. The solid particles then flow upwardly and concurrentlywith the hot gases introduced through the inlet 12 to the separator 13.The solid particles are discharged from the separator 13 through theoutlet 14. The volume of gases introduced into the riser 10 and the sizeof the riser 10 is such that the velocity of the gas stream will suspendthe fine particle size materials and convey them to the separator 13.This velocity is dependent largely upon the particle size and density ofthe fine ore. In actual practice, I have found that a velocity greaterthan 10 feet per second is usually required to prevent particles offerruginous ore from settling out of the gas stream due to the forces ofgravity.

It will thus be seen that the solid particles and gas flow concurrentlyas they pass upwardly through the risers 10 and 11 whereby the solidparticles are suspended in the moving gases. However, the overall flowof the solids is countercurrent to the flow of gases. That is to say,the sol-id particles are introduced into the lower end of the secondriser 11 and are then passed through the first riser 10 before beingdischarged. Accordingly, the second riser 11 senves as a preheater whilethe first riser 10 serves as a reactor. Since down flow of solidmaterials in conduit 28 is essential to the maintenance of pressurebalance and proper direction of gas flow, the introduction of solids at26 must be started at a relatively low rate .and gradually increased tothe proper operating level. Also, if desired, a suitable valve may beprovided in conduit 28 whereby the flow of gas through conduit 28 isrestrained until the system is placed in operation. That is, the valve25 would be gradually moved to open position after a solids feed ratehas been established. Also, the solid-s discharge outlet 14 is connectedto a solids discharge system which restricts the flow of gas into andout of the system. As the solids flow upwardly concurrently with the gasstream, gravity restrains upward movement of the larger particle sizematerials more than it restrains upward movement of the smaller particlesize materials whereby the larger particle size materials are subjectedto longer exposure to the hot gases thereby bringing about the requiredroasting of the larger particle size materials.

Unless counteracted, the gas introduced at inlet 12 will tend to passupwardly through the solids downcomer 28 to the separator 19, therebyshort-circuiting the reaction zone and greatly lowering the separatingefiicie-ncy of the separator 19. That is, because of frictional lossesin the system, the gas at the inlet will be at a higher pressure thanthe gas within the separator 19, unless counteracted. The desired flowof gas is through the venturi 23 and upwardly through the first riser 10to the separator 13 and then downwardly through the conduit 17 to thelower end of the second riser '11 where the gas flows upwardlytherethrough and is finally discharged through the outlet 21. Thisproblem cannot be solved by providing a mechanical air-lock device, suchas a rotary feeder or a gravity trickle valve due to the fact that suchdevices would not be satisfactory for use at temperatures employed forthe reduction of iron.

In accordance with my invention, I provide a venturi and select aventuri throat configuration such that where gas alone is flowingthrough the system, the pressure drop of the gas flowing through thedesired path in my apparatus is almost completely equalled by theventuri pressure change so that essentially no pressure exists to causefiow of gas upwardly through the conduit or solids downcomer 28. Inactual practice, I find that when solids are being conveyed by gas in myapparatus, the pressure drop through the desired path is increased whilethe differential of pressure brought about by the venturi is notmaterially affected by the presence of solids. I have also found that byproper choice of the diameter and length of the solids downcomer 28, thesolids falling down the solids downcomer 28 will increase the gaspressure near the bottom of the downcomer and shortcircuiting of gas,when the system is conveying solids, can be prevented.

The pressure developed by solids falling in a standpipe is important inthe function of my multi-stage system due to the fact that the solidparticles flow down the downcomer 28. I have found that the gas pressuredeveloped at the bottom of a standpipe by the flow of solids is directlyproportional to the length of the standpipe. FIG. 2 of the drawingsshows that the pressure developed also increases with the increasingrate of solids flow and decreasing pipe diameter. The iron ore employedin obtaining the results shown in FIG. 2 was minus 20 mesh iron. Thecurves show that the pressure developed is much reduced in largerdiameter pipe, such as would be used in commercial operation. However, acompensating factor is that the resistance offered to gas flow in theriser and other parts of the system will also be reduced in largerdiameter pipes, as shown by the dashed line in FIG. 2. Accordingly, thepressure developed by falling solids would be equally useful in a largecommercial system to prevent upward flow of gas through the solidsdowncomer 28. The pressure developed is indicated in FIG. 2 by inches ofwater, on the water gauge, over the length of the conduit, measured infeet. Thus, by properly selecting the length and width of the downcomer,a pressure increase can be developed, from the top to the bottom of thedowncomer, equal to the pressure decrease caused by conveying solidsthrough portions of the desired path in the apparatus.

Referring now to FIG. 3 of the drawings, I show the complete treatmentof the materials in a rnulti-stage system. The crushed ore is stored ina suitable bin 29 and is transferred to a dry-grinding system indicatedgenerally at 31 whereby the ore is pulverized and dried simultaneously.The particle size to which the ore must be crushed to effect rapidreaction is determined by the physical characteristics of the naturalore. That is, some natural ores have a porous structure which permitssome penetration of gas into the interior of the particles. These oreswill reduce rapidly at a muchcoarser size than will an ore having adense structure. In actual practice, I have found that many ores can bereduced in my improved apparatus by crushing the ores to a particle sizewhereby the largest particles will pass a standard mesh testing sieve.

The finely pulverized ore passes from the grinding system 31 to an airclassifier 32 and then to a cyclone separator 33 where exhaust gases areremoved as at 34. The pulverized ore is stored in a bin 36 and is thenconveyed through a supply line 37 to an upwardly extending riser 38which communicates at its upper end with a cyclone separator 39. Theexhaust gases from the separator 39 are removed through a conduit 41where they are conveyed through the grinding system 31, the airclassifier 32 and the separator 33 whereby the gases dry the oreintroduced into the grinding system. The fine particle size materialsintroduced into the riser 38 thus move concurrently and in suspensionwith the gaseous stream to the separator 39'.

The gaseous stream supplied to the line 38 comes from the exhaust of acyclone separator 42. The fine particle size ore materials dischargedfrom the lower end of the cyclone separator 39 enter a line 43 and arethen discharged into a riser 44 which communicates the gas exhaust of acyclone separator 45 with the cyclone separator 42. The upwardly movingstream of gas in the riser 44 picks up the fine particle size orematerials whereby they are suspended in the gas and conveyedconcurrently therewith to the separator 42.

Communicating with the cyclone separator 45 is the upper end of riser46. The lower end of the riser 46 communicates with a line 47 whichsupplies the gaseous stream from a gas generator 43. Solid materialsdischarged from the separator 42 are introduced into the lower end ofthe riser 46 by a line 49 whereby they move upwardly and concurrently insuspension with the gaseous stream to the separator 45. The reducinggases formed in the gas generator 48 may be provided by introducing airthrough a conduit 51 and natural gas through a conduit 52 whereby theyare mixed and partially burned in the gas generator 48 prior to beingintroduced into the riser 46. The composition and temperature of thegases leaving the generator 48 may be controlled by recycling a portionof the gaseous stream exhausted from the cyclone separator 42 through aline 53 to the air supply line 51.

The movement of the fine particle size ore materials through the risers38 and 44 serves as a temperature preparation whereby the ore ispreheated prior to being introduced into the riser 46 carrying the hotreducing gases. The fine particle size materials to be roasted are fedthrough the apparatus at a suitable rate whereby the particles aresuspended completely in the reducing gases while passing through theriser 46. The riser 46 thus serves as a reaction zone whereby the fineparticle size materials are not only suspended in this zone but flowconcurrently with the reducing gases to the separator 45. The volume ofthe reducing gases introduced in the riser 46 and the size of the riser46 is such that the velocity of the gas stream will suspend the fineparticle size materials and convey them to the separator 45. As the oreparticles pass through the separator 45, they are separated and aredischarged into a cooler 54.

From the cooler 54, the reduced ore passes to suitable magneticseparators indicated generally at 56 whereby the magnetic materials areseparated from the non-mag netic materials. The magnetic ore may thenpass to suitable briquetting or pelletizing apparatus 57 in a mannerwell understood in the art.

In view of the fact that the fine particle size ore to be reduced andthe hot reducing gases are flowing concurrently, it is desirable to havethe ratio of reducing gases and the iron oxides at least equal to thatrequired to produce the desired chemical reaction. That is, since thereaction occurs in the zone of the risers 10 and 46, it is necessarythat the quantity of reducing gas introduced into these risers besufficient to reduce all of the iron contained in the ore to the desiredoxide.

In order to convert one pound of hematite to magnetite, approximately0.8 cubic feet of either carbon monoxide or hydrogen (dry basis, 60 F.,29.92 inches of mercury) is required. Where the reducing gas contains15% carbon monoxide or hydrogen at a temperature of approximately 1400F. and atmospheric pressure, the gas volume required for one pound ofhematite is approximately 19 cubic feet. Approximately this volume ofgas is required to suspend one pound of hematite and the other materialsassociated therewith in the natural ore.

The suspension of fine particle size materials in reducing gases ismaintained at an elevated temperature which is below the fusion point ofthe various components of the material. That is, it is desirable toprevent the particles from passing into the liquid or melted stateduring the reaction. The relationship of the size of the fine particlesize materials to the velocity of the reducing gases is maintained at orabove a value which prevents any particles of the ore from settling outof the gaseous stream due solely to the action of gravity.

As an example of the operation of my apparatus, an iron ore containing43.6% iron was crushed to pass a 14 mesh testing sieve. This ore wasreduced in a two-stage apparatus similar to that shown in FIG. 1 inwhich the risers were of standard 1% inch pipe approxiately 7 feet long.The reducing gas contained 16.5% carbon monoxide and hydrogen. Themeasured temperature of the gas was maintained at approximately 1540 F.Essentially complete reduction of the iron oxide to magnetite wasobtained at an ore rate of approximately 188 pounds per hour and a gasrate of 10 standard (60 F., 29.92 inches of mercury) cubic feet perminute.

From the foregoing, it will be seen that I have devised improvedapparatus for treating ore-like materials, such as ferruginous ores.While I have described my apparatus as being particularly adapted foruse in treating ferruginous ores, it will be apparent that it is adaptedfor roasting other materials, such a pyrite and the like. By roastingthe fine particle size materials while they are in complete suspensionin the hot gases, the roasting or reduction takes place in a minimum oftime. Also, by constructing and arranging the apparatus whereby thepressure drop of gas flowing through the risers and the equipmentassociated therewith is substantially equal to the change of pressure atthe venturi in the first riser and that created by solids flowing downthe solids downcomer, there is substantially no pressure drop across thesolids downcomer to cause flow of gas directly from the gas inlet to theseparator associated with the second riser.

I wish it to be understood that my improved apparatus is adapted foroperation under a wide range of conditions, as will be apparent to oneskilled in the art, and is not liimted to any specific proportions ofgases to solids.

While I have shown my invention in two forms, it will be obvious tothose skilled in the art that it is not so limited but is susceptible ofvarious other changes and modifications without departing from thespirit thereof, and I desire, therefore, that only such limitationsshall be placed thereupon as are specifically set forth in the appendedclaims.

What I claim is:

1. Apparatus for reducing fine particles of solid material, saidapparatus comprising:

a first upwardly extending riser;

first separator means, adjacent the upper end of said first riser, forseparating particles of solid material from gas;

a second upwardly extending riser;

second separator means, adjacent the upper end of said second riser, forseparating particles of solid material from gas;

means communicating the lower portion of said second riser with saidfirst separator means and in position to receive gas discharged fromsaid first separator means;

means for supplying a continuously moving stream of heated reducing gasto the lower end of said first riser; said first riser, said firstseparator means, said communicating means, said second riser and saidsecond separator means defining a path for the passage of said gas fromthe first riser through the first separator to the second separator;means for introducing particles of solid material tobe-reduced into saidsecond riser adjacent the lower portion thereof, whereby said particlesare fully suspended in a dilute, finely divided state in said stream ofgas moving upwardly through the second riser for movement concurrentlywith said gas to said second separator means; substantially unobstructedconduit means, extending downwardly from said second separator means toa junction with the lower portion of said first riser, for transferringparticles of solid material separated in said second separator means tosaid first riser, whereby said particles are fully suspended in adilute, finely divided state in said upwardly moving stream of gas insaid first riser for movement concurrently with said gas to said firstseparator means;

said first riser extending upwardly from said junction;

and means, at the junction of said downwardly extending conduit meansand said first riser, for providing a pressure drop at said junctionequal to the pressure drop of gas moving along said path, wherebymovement of gas through said downwardly extending conduit means isimpeded;

said apparatus including means for maintaining the velocity of saidstream of gas at a value to convey said particles continuously in anupward direction through said risers and to prevent said particles fromsettling out of said stream by the action of gravity alone; 7

and means for removing said particles from said first separator means.

2. Apparatus as recited in claim 1 wherein said pressure-drop means atsaid junction comprises a venturi throat in communication with saiddownwardly extending conduit means for receiving said particles of solidmaterial.

3. Apparatus as recited in claim 1 wherein said downwardly extendingconduit means has a cross-sectional area and length constituting meansfor providing a pressure increase in said conduit means from the secondseparator means to said junction, when said particles of solid materialfall through said conduit means, equal to the pressure drop caused bysaid particles moving, with said gas, through the apparatus alongportions of said path, whereby movement of gas through said downwardlyextending conduit means is prevented.

4. Apparatus for reducing fine particles of solid material, saidapparatus comprising:

a first upwardly extending riser;

first separator means, adjacent the upper end of said first riser, forseparating particles of solid material from gas;

a second upwardly extending riser;

second separator means, adjacent the upper end of said second riser, forseparating particles of solid material from gas;

means communicating the lower portion of said second riser with saidfirst separator means and in position to receive gas discharged fromsaid first separator means;

means for supplying a continuously moving stream of heated reducing gasto the lower end of said first riser;

said first riser, said first separator means, said communicating means,said second riser and said second separator means defining a path forthe passage of said gas from the first riser through the first separatorto the second separator;

means for introducing particles of solid material tobe-reduced into saidsecond riser adjacent the lower portion thereof, whereby said particlesare fully suspended in a dilute, finely divided state in said stream ofgas moving upwardly through the second riser for movement concurrentlywith said gas to said second separator means;

substantially unobstructed conduit means, extending downwardly from saidsecond separator means to a junction with the lower portion of saidfirst riser, for transferring particles of solid material separated insaid second separator means to said first riser, whereby said particlesare fully suspended in a dilute, finely divided state in said upwardlymoving stream of gas in said first riser for movement concurrently withsaid gas to said first separator means;

said first riser extending upwardly from said junction;

said downwardly extending conduit means having a cross-sectional areaand length constituting means for providing a pressure increase in saidconduit means from the second separator means to said junction, whensaid particles of solid material fall through said conduit means, equalto the pressure drop caused by said particles moving, with said gas,through the apparatus along portions of said path, whereby movement ofgas through said downwardly extending conduit means is impeded;

said apparatus including means for maintaining the velocity of saidstream of gas at a value to convey said particles continuously in anupward direction through said risers and to prevent said particles fromsettling out of said stream by the action of gravity alone;

and means for removing said particles from said first separator means.

5. In an apparatus for treating fine particles of solid material:

a first upwardly extending riser;

a second upwardly extending riser;

separator means, adjacent the upper end of said second riser, forseparating solid particles from gas;

gas passage means communicating the lower portion of said second riserwith the upper portion of said first riser;

means for supplying a continuously moving stream of gas to the lower endof said first riser;

said first riser, said gas passage means, said second riser and saidseparator means defining a path for the movement of said gas from thefirst riser through the second riser to the separator means;

means for introducing fine particles of solid material into said secondriser adjacent the lower portion thereof, whereby said particles arefully suspended in a dilute, finely divided state in said stream of gasmoving upwardly through the second riser, for movement of said particlesconcurrently with said gas to said separator means;

substantially unobstructed conduit means, extending downwardly from saidsecond separator means to a junction with the lower portion of saidfirst riser, for transferring particles of solid material separated insaid separator means to said first riser, whereby said particles arefully suspended in a dilute, finely divided state in said upwardlymoving stream of gas in said first riser for movement concurrently withsaid gas in said first riser;

said first riser extending upwardly from said junction;

and means, at the junction of said downwardly extending conduit meansand said first riser, for providing a pressure drop at said junctionequal to the pressure drop of gas moving along said path, wherebymovement of gas through said downwardly extending conduit means isimpeded;

said apparatus including means for maintaining the velocity of saidstream of gas at a value to convey said particles continuously in anupward direction through said risers and to prevent said particles ofmaterial from settling out of said stream by the action of gravityalone,

said gas passage means including a gas-solids separator at the top ofthe first riser.

6. Apparatus as recited in claim wherein said pressure-drop means atsaid junction comprises a venturi throat in communication with saiddownwardly extending conduit means for receiving said particles of solidmaterial.

7. Apparatus as recited in claim 5 wherein said downwardly extendingconduit means has a cross-sectional area and length constituting meansfor providing a pressure increase in said conduit means from theseparator means to said junction, when said particles of solid mate rialfall through said conduit means, equal to the pressure drop caused bysaid particles moving, with said gas, through the apparatus alongportions of said path, whereby movement of gas through said downwardlyextending conduit means is prevented.

8. In an apparatus for treating fine particles of solid material:

a first upwardly extending riser;

a second upwardly extending riser;

separator means, adjacent the upper end of said second riser, forseparating solid particles from gas;

gas passage means communicating the lower portion of said second riserwith the upper portion of said first riser;

means for supplying a continuously moving stream of gas to the lower endof said first riser;

said first riser, said gas passage means, said second riser and saidseparator means defining a path for the movement of said gas from thefirst riser through the second riser to the separator means;

means for introducing fine particles of solid material into said secondriser adjacent the lower portion thereof, whereby said particles arefully suspended in a dilute, finely divided state in said stream of gasmoving upwardly through the second riser, for movement of said particlesconcurrently with said gas to said separator means;

substantially unobstructed conduit means, extending downwardly from saidsecond separator means to a junction with the lower portion of saidfirst riser, for transferring particles of solid material separated insaid separator means to said first riser, whereby said particles arefully suspended in a dilute, finely divided state in said upwardlymoving stream of gas in said first riser for movement concurrently withsaid gas in said first riser;

said first riser extending upwardly from said junction;

said downwardly extending conduit means having a cross-sectional areaand length constituting means for providing a pressure increase in saidconduit means from the separator means to said junction, when saidparticles of solid material fall through said conduit means, equal tothe pressure drop caused by said particles moving, with said gas,through the apparatus along portions of said path, whereby movement ofgas through said downwardly extending conduit means is impeded;

said apparatus including means for maintaining the velocity of saidstream of gas at a value to convey said particles continuously in anupward direction through said risers and to prevent said particles ofmaterial from settling out of said stream by the action of gravityalone;

said gas passage means including a gas-solids separator at the top ofthe first riser.

References Cited by the Examiner UNITED STATES PATENTS Re. 17,212 2/1929Stockton 263--21 1,310,455 7/1919 Tainton -9 2,274,789 3/1942 Horesi3410 X 2,343,780 5/1944 Lewis 75-26 2,559,551 7/1951 Weber 34-10 X2,683,077 7/1954 Lewis 759 X 2,757,921 8/1956 Petersen.

2,821,471 7/1958 Sellers 7526 3,03 1,293 4/1962 Meissner 7526 FOREIGNPATENTS 775,356 5/1957 Great Britain.

OTHER REFERENCES Zenz et al.: Fluidization and Fluid Particle Systems,pp. 158160, 343-345, Reinhold Publ. Corp., New York, 1960.

WHITMORE A. WILTZ, Primary Examiner.

WINSTON A. DOUGLAS, DELBERT E. GANTZ,

MORRIS WOLK, Examiners.

1. APPARATUS FOR REDUCING FINE PARTICLES OF SOLID MATERIAL, SAIDAPPARATUS COMPRISING: A FIRST UPWARDLY EXTENDING RISER; FIRST SEPARATORMEANS, ADJACENT THE UPPER END OF SAID FIRST RISER, FOR SEPARATINGPARTICLES OF SOLID MATERIAL FROM GAS; A SECOND UPWARDLY EXENDING RISER;SECOND SEPARATOR MEANS, ADJACENT THE UPPER END OF SAID SECOND RISER, FORSEPARATING PARTICLES OF SOLID MATERIAL FROM GAS; MEANS COMMUNICATING THELOWER PORTION OF SAID SECOND RISER WITH SAID FIRST SEPARATOR MEANS ANDIN POSITION TO RECEIVE GAS DISCHARGED FROM SAID FIRST SEPARATOR MEANS;MEANS FOR SUPPLYING A CONTINUOUSLY MOVING STREAM OF HEATED REDUCING GASTO THE LOWER END OF SAID FIRST RISER; SAID FIRST RISER, SAID FIRSTSEPARATOR MEANS, SAID COMMUNICATING MEANS, SAID SECOND RISER AND SAIDSECOND SEPARATOR MEANS DEFINING A PATH FOR THE PASSAGE OF SAID GAS FROMTHE FIRST RISER THROUGH THE FIRST SEPARATOR TO THE SECOND SEPARATOR;MEANS FOR INTRODUCING PARTICLES OF SOLID MATERIAL TOBE-REDUCED INTO SAIDSECOND RISER ADJACENT THE LOWER PORTION THEREOF, WHEREBY SAID PARTICLESARE FULLY SUSPENDED IN A DILUTE, FINELY DIVIDED STATE IN SAID STREAM OFGAS MOVING UPWARDLY THROUGH THE SECOND RISER FOR MOVEMENT CONCURRENTLYWITH SAID GAS TO SAID SECOND SEPARATOR MEANS; SUBSTANTIALLY UNOBSTRUCTEDCONDUIT MEANS, EXTENDING DOWNWARDLY FROM SAID SECOND SEPARATOR MEANS TOA JUNCTION WITH THE LOWER PORTION OF SAID FIRST RISER, FOR TRANSFERRINGPARTICLES OF SOLID MATERIAL SEPARATED IN SAID SECOND SEPARATOR MEANS TOSAID FIRST RISER, WHEREBY SAID PARTICLES ARE FULLY SUSPENDED IN ADILUTE, FINELY DIVIDED STATE IN SAID UPWARDLY MOVING STREAM OF GAS INSAID FIRST RISER FOR MOVEMENT CONCURRENTLY WITH SAID GAS TO SAID FIRSTSEPARATOR MEANS; SAID FIRST RISER EXTENDING UPWARDLY FROM SAID JUNCTION;AND MEANS, AT THE JUNCTION OF SAID DOWNWARDLY EXTENDING CONDUIT MEANSAND SAID FIRST RISER, FOR PROVIDING A PRESSURE DROP AT SAID JUNCTIONEQUAL TO THE PRESSURE DROP OF GAS MOVING ALONG SAID PATH, WHEREBYMOVEMENT OF GAS THROUGH SAID DOWNWARDLY EXTENDING CONDUIT MEANS ISIMPEDED; SAID APPARATUS INCLUDING MEANS FOR MAINTAINING THE VELOCITY OFSAID STREAM OF GAS AT A VALUE TO CONVEY SAID PARTICLES CONTINUOUSLY INAN UPWARD DIRECTION THROUGH SAID RISERS AND TO PREVENT SAID PARTICLESFROM SETTLING OUT OF SAID STREAM BY THE ACTION OF GRAVITY ALONE; ANDMEANS FOR REMOVING SAID PARTICLES FROM SAID FIRST SEPARATOR MEANS.